Proper spermatid development is required for male fertility. To produce sperm competent for fertilization, the developing spermatid undergoes radical changes in cell shape and structure, yet little is known about the genetic contributions and molecular mechanisms required for spermatid morphogenesis. Recent evidence makes clear that the actin related protein, Actin like 7B (ACTL7B), is critical for this process. The goa of the current study is to define the mechanism by which ACTL7B mediates spermiogenesis to better understand both mechanisms of Actin Related Protein (ARP) function and to understand how fertilization competent sperm are produced. Infertility affects approximately ten percent of couples with half of these cases linked to the male, however nearly half of the cases of male infertility are idiopathic with unknown causes. This study will test the hypothesis that ACTL7B plays a role in regulation and organization of the actin cytoskeleton for functional spermatid morphogenesis and male fertility. The molecular associations of ACTL7B with proteins or protein complexes within developing spermatids will be determined, the ability of ACTL7B to directly affect actin filament organization and dynamics will be assessed, and the role of F-actin dynamics in developing spermatids will be investigated in testis explants. These studies will aid in understanding of actin related protein functions and specifically the role of ARPs in spermatogenesis to produce viable sperm for healthy perpetuation of life.